>So, what, some time after the line, after a sale was made, during fulfillment, a Chinese super-spy managed to open up specific server that the juicy target was getting and solder some special chip onto the board somehow in a way that worked instead of bricking the board?

I'm not sure why you're implying that you need a super-spy to pull this off. If this was done at the factory level they likely had access to the same manufacturing equipment used to make the motherboards, so there's no need to manually solder anything. The implant was alleged to be a surface-mount component so it could be as simple as reprogramming the pick-and-place machine or swaping out the reels. Given that this is china enlisting a couple of technicians to your cause wouldn't be too hard[1]. From there once they figure out a particular order is going to a juicy target they can ship the bugged boards in place of the untampered boards.

> But you need actual evidence for such a tale.

Agreed. My main takeway from the article is that this hack could happen, not necessarily that it has happened.

[1] it's not unlike the concerns that there are NSA backdoors in intel cpus (eg. AMT/vpro, or RDRAND), or windows (NSAKEY).